Every time electrical current is to be transferred between two separate members of a mechanical device, some form of contact unit is required. When the two members do not need to be in physical contact with each other, electrical contact is often made by means of an electrical cord, whose one end is electrically connected with the one member and whose other end is provided with a plug. The second member is provided with a socket, into which the plug fits. The plug constitutes a male member, with pins which extend from its body. The socket constitutes a corresponding female member.
When the two members must be in physical contact with each other, for example when the second member is to be mounted on the first, this type of electrical contact is often unsatisfactory, especially if the mounting surfaces are mainly flat. Although the electrical cord could be led from a side surface of the first member to a socket in a side surface of the second member, this leads to an extra work step; furthermore, the cord may be inadvertantly pulled out or otherwise damaged.
A particular problem arises if the second member is not provided with a socket. This may for example be the case when an old accessory, which does not include or use electrical and electronic components, is to be mounted on a new main member which does. This is so in the case of modern system cameras which have interchangeable film magazines when one wishes to mount a magazine without an electrical socket, i.e., with no need for an electrical contact, onto a camera housing, which is equipped with electronic and electrical contact devices. In such case, the cord will either hang loose or its contacts or connection points with the main member will remain unprotected.
One way to avoid the disadvantages of a cord connection is to arrange male and female contacts respectively in the camera housing itself and the magazine itself. When the magazine is mounted on the housing, the male contacts are carefully guided into the female contacts. In addition to the need for great care in order to avoid damaging the male contacts, this solution suffers from another significant disadvantage. Since the contact pins extend from the mounting surface, if the male contacts are securely mounted in the camera housing, it is impossible to mount a magazine which does not have holes, i.e. female contacts, into which the pins may fit. This precludes the use of old magazines, which do not include electronics, or of other magazines which are not provided with receiving female contacts or holes.
One known to solution to this problem is to mount the pins of the male contact member in holes in the camera housing, whereby springs bias the pins outward so that they extend out from the mounting surface of the camera housing. When a magazine without receiving female contacts is mounted on the camera housing, the pins are pushed into the camera housing by the flat mounting surface of the magazine. The disadvantage of this solution is that the ends of the pins will always be pressed against the mounting surface of the magazine. Since this mounting surface is not a contact surface, the tips of the pins, which constitute the contact surfaces of the pins, easily becomes soiled and are subjected to unnecessary wear. It is therefore advantageous to have a male contact member which makes it possible for the contact pins to retract when an accessory lacking receiving female contacts is mounted on the main member.
U.S. patent application Ser. No. 07/244,264 describes a contact cradle in which contact pins are pushed out of the way when a supporting surface on the accessory--in the described case a camera lens--presses against a roller in the contact cradle. When the lens approaches a contact position the roller rolls into a recess in the supporting surface of the lens. Under the influence of a spring, the cradle then rotates about an axle so that the contact pins are pressed against the corresponding female contacts in the lens. This contact arrangement is primarily intended for use with accessories which are mounted on a main member by means of a rotational movement. The contact cradle itself also moves between its different positions by rotation. It furthermore requires rollers, so that the contact cradle must be at least as wide as the roller. Finally, this contact arrangement has no switch or contact by means of which it is possible for the electronic system of the camera to determine whether a mounted lens is provided for electrical contact with the camera housing.
Accordingly, one object of the present invention it to provide an electrical contact unit by means of which two members may be electrically connected, and whose contact elements ensure good electrical contact when both the members are provided for electrical connection, whereas the male contacts are securely retracted in order to avoid damage and wear when the main members are not so provided. Another object is to arrange the contact unit so that it is possible to determine whether an accessory is mounted on the main member.